37 year old poop tank- Oh boy

[Barking Sands]

I never noticed any leaks from the holding tank. Never any smell. I am thinking this area was blocked partially by dried "stuff". I looked at this holding tank several times after using it and just never saw anything leak. Very odd. But I always knew I would need to tackle this sooner than later. So I pulled the tank and ordered new hose. After cleaning the tank I noticed this extensive corrosion on the bottom layer. It appears to be 316 stainless. I have filled in these areas as well as half a dozen other sites on the bottom layer that are not as bad. I am using ER316L stainless wire through the Miller Mig with 75/25. I am not the best welder in the world and so far it aint pretty. But after one round of filling I am down to about 5 leaks that are now pin hole sized (checked with air pressure and Snoop). A bit more grinding and filling and it should be leak free.

If this doesnt work out I have a plastic tank picked out. However I would rather get this tank back in shape since it is a custom fit to a very small space.

Oh the joys of boat repair. You havent lived until you weld on a used poop tank :lol:

 

[Comodave]

You may get it fixed temporarily but it will keep happening. Metal and holding tanks don’t go together. Get a quality plastic tank and be done with it. Ronko makes good ones, no affiliation.

 

[O C Diver]

Custom size holding tanks are available at a reasonable price, so it's no longer about capacity.

Ted

 

[RT Firefly]

Greetings,
Mr. BS. How about, after you get all the welding done, you coat the inside and the outside with one of the tank sealers often mentioned on TF usually in conjunction with fuel tank leaks? (Can't remember brand names-Hopefully you know what I'm referring to). Might buy you some more time...

 

[mvweebles]

. I am using ER316L stainless wire through the Miller Mig with 75/25. I am not the best welder in the world and so far it aint pretty.

You will be soon. Plenty of ongoing opportunity to practice here as it will be increasingly hard to stay ahead. Sort of like bailing a leaky boat with a colander instead of a bucket.

Peter
View attachment 125935

 

[Barking Sands]

Yes..after sleeping on it I am leaning on replacing with a plastic unit. I was thinking I could mount a strong LED light behind the tank with a switch to check tank levels. Looking forward to getting this job done.

 

[jleonard]

Greetings,
Mr. BS. How about, after you get all the welding done, you coat the inside and the outside with one of the tank sealers often mentioned on TF usually in conjunction with fuel tank leaks? (Can't remember brand names-Hopefully you know what I'm referring to). Might buy you some more time...

Eastwood fuel tank sealer is probably what you are referring to.
I used the kit on the outside of my Albin fuel tanks. Good stuff.

 

[OldDan1943]

Yup plastic is the way to go.
You can continue practicing welding on the tank for future use.
Per the light, a nice feature if you do not have a tank minder system.

 

[HeadedToTexas]

You may get it fixed temporarily but it will keep happening. Metal and holding tanks don’t go together. Get a quality plastic tank and be done with it. Ronko makes good ones, no affiliation.

Seems like the real impediment to holding tank replacement is getting the old tank out and the new tank in. Looks like you've got that part already solved. Go plastic for sure.

 

[Crux]

Nice work and good to see folks handling things!

How about this....make a stainless plate, say 8" square, that would reach out to solid area of tank.....weld hose elbow to plate such that in same location.....weld plate to tank....or bolt down to provide a removable access plate?

 

[rslifkin]

Don't bother welding it. Metal holding tanks don't last, so you're guaranteed to have more spots that aren't leaking yet, but are very close. New tank should be either plastic or fiberglass, both of those hold up much better to corrosive urine.


You can get custom shaped plastic tanks made in unusual shapes if an off the shelf one isn't a good fit. For odd shapes, you can also build a tank in fiberglass. Either build to shape and install, or you can build in place if there's no way to get the whole tank in and out.

 

[OldDan1943]

Nice work and good to see folks handling things!

How about this....make a stainless plate, say 8" square, that would reach out to solid area of tank.....weld hose elbow to plate such that in same location.....weld plate to tank....or bolt down to provide a removable access plate?

Crux, if he were out in the wilderness, sure weld. He' is in town, has the tank out, that is the hard part. If he orders a custom tank, the manufactory will install the threaded connectors where you want.

 

[OldDan1943]

Now, the material selected for the pump out tube is important too. I had that go bad on my N46.

 

[rslifkin]

Now, the material selected for the pump out tube is important too. I had that go bad on my N46.

I used PVC pipe for the dip tube in my plastic tank.

 

[Crux]

Crux, if he were out in the wilderness, sure weld. He' is in town, has the tank out, that is the hard part. If he orders a custom tank, the manufactory will install the threaded connectors where you want.

Yep, gotcha......but he has a welder....most who do like to fabricate...fun stuff to those so inclined....I dig it!

 

[HeadMistress]

I'm amazed that any metal waste tank could have lasted that long...urine typically turns the bottom into a colander in about 10 years. Aluminum was the original material of choice because it was cheap...steel was an expensive upgrade. States didn't even begin enacting legislation to enforce marine sanitation laws until the late '80s, and those that did were slow to enforce them, so most tanks installed by builders often weren't used until the late '90s and even beyond. By then the industry had recognized that metal was not the right choice for waste holding and had switched to plastic the recommended material. So I'm guessing that your tank has only been used for 15 years at most. Its bottom IS turning into a colander. Replace it before you'll not only have no choice, but also have to deal with cleanup and odor from the leak(s).


Ronco Plastics Ronco Plastics marine Tanks is your best source for a tank. They make TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank. There are retailers who sell Ronco tanks, but Ronco sells direct for a much lower price...and they're great to work with.

When looking at drawings it's important to know that there is no top or bottom until the fittings go in, and YOU decide where they go. So rotate, flip in any orientation to find the tank that fit your space.


If you have no choice but to go with a custom tank, Triple M Plastics in Maine is your best choice. About twice the cost of a rotomolded tank, but worth every penny. Triple M Plastic Products Inc



--Peggie

 

[RT Firefly]

Greetings,
Mr. jl. My memory is SO bad. Thanks. What was the question again???

 

[OldDan1943]

I used PVC pipe for the dip tube in my plastic tank.

Yea, probably if it is a direct connection. The N46 had a stainless plate and the stainless steel pump out tube was threaded into that.

 

[Barking Sands]

Don't bother welding it. Metal holding tanks don't last, so you're guaranteed to have more spots that aren't leaking yet, but are very close. New tank should be either plastic or fiberglass, both of those hold up much better to corrosive urine.

I actually thought about fiberglassing around this stainless tank. But then if it still corroded through and the fiberglass separated from the tank that would be an even larger nightmare with pockets of sewage . Not to mention when you start talking about fiberglassing or adding additional plates (which I did ponder) or anything like that you are now getting into real work. If it just had a few pinholes that I could tack weld shut I would probably have put this back in. But the nature of the corrosion in the photo tells a different story. I could take it to work and measure thickness with ultrasound and do further NDT for hidden pockets of corrosion but again...all too much to save a 37 year old poop tank that was never great to start with.

What is the life expectancy of the newer plastic tanks?

Did I say I am looking forward to being done with this project...lol.

 

[rslifkin]

I'm amazed that any metal waste tank could have lasted that long...urine typically turns the bottom into a colander in about 10 years.

I'm surprised as well, but the original aluminum holding tank in my boat made it almost 34 years before developing a single pinhole. I'm sure it was getting close to much worse failures though. Oddly, the fresh water tank I pulled out this winter had far worse corrosion (due to poor mounting and the underside getting wet, leading to severe corrosion). I kinda wonder what conditions lead to the occasional long lasting metal tank in this application, considering how corrosive the contents are to most metals you'd use in a tank.

 

[Barking Sands]

I'm amazed that any metal waste tank could have lasted that long...urine typically turns the bottom into a colander in about 10 years. Aluminum was the original material of choice because it was cheap...steel was an expensive upgrade. States didn't even begin enacting legislation to enforce marine sanitation laws until the late '80s, and those that did were slow to enforce them, so most tanks installed by builders often weren't used until the late '90s and even beyond. By then the industry had recognized that metal was not the right choice for waste holding and had switched to plastic the recommended material. So I'm guessing that your tank has only been used for 15 years at most. Its bottom IS turning into a colander. Replace it before you'll not only have no choice, but also have to deal with cleanup and odor from the leak(s).


Ronco Plastics Ronco Plastics marine Tanks is your best source for a tank. They make TOP quality thick-walled water and waste tanks for a very reasonable price and have more than 400 shapes and sizes, over 100 of which are non-rectangular, and they install fittings in the sizes and locations specified by the customer when they make the tank. There are retailers who sell Ronco tanks, but Ronco sells direct for a much lower price...and they're great to work with.

When looking at drawings it's important to know that there is no top or bottom until the fittings go in, and YOU decide where they go. So rotate, flip in any orientation to find the tank that fit your space.


If you have no choice but to go with a custom tank, Triple M Plastics in Maine is your best choice. About twice the cost of a rotomolded tank, but worth every penny. Triple M Plastic Products Inc



--Peggie

Thanks a bunch for your input. Ronco is the tank that I had selected. Glad to hear your endorsement. They have an off the shelf tank that is within 1/2 inch of the dimensions of this original tank. I am ordering from Tank Depot. I already bought Sani-Flex hose. I will also be adding a shut off valve just under the tank to contain waste that would otherwise fill the overboard discharge hose that leads to the seacock drain fitting. This tank is up above the water line and the overboard drain is gravity feed. The way it is now even if you pump out that lowest section of hose remains filled. The shut off valve just below the tank should keep that section of hose from remaining full.

Any other last minute advice of things I may need to order?

 

[Barking Sands]

Yep, gotcha......but he has a welder....most who do like to fabricate...fun stuff to those so inclined....I dig it!

Me too..lol. I love to do things myself. But one night of welding on a partially cleaned poop tank has realigned my outlook on this project. :lol:

 

[HeadMistress]

Oddly, the fresh water tank I pulled out this winter had far worse corrosion (due to poor mounting and the underside getting wet, leading to severe corrosion).


The average life of aluminum water tanks is about 20 years because it takes about that long for the chlorine in municipal water supplies to corrode them enough to start leaking...which is why adding a little bleach to each fill is a very bad idea.


I have no idea why your water and waste tanks have beaten the odds by as much as they have....the exception that proves every rule, I guess.


--Peggie

 

[rslifkin]

Oddly, the fresh water tank I pulled out this winter had far worse corrosion (due to poor mounting and the underside getting wet, leading to severe corrosion).


The average life of aluminum water tanks is about 20 years because it takes about that long for the chlorine in municipal water supplies to corrode them enough to start leaking...which is why adding a little bleach to each fill is a very bad idea.


I have no idea why your water and waste tanks have beaten the odds by as much as they have....the exception that proves every rule, I guess.


--Peggie

Yeah, I don't know why they lasted so long either. And when I shoved a camera into the water tank, it only showed minor corrosion inside despite 36 years of chlorinated tap water (and probably some added bleach here and there). The corrosion that perforated the bottom and caused it to leak was from the outside (it was stupidly mounted flat on a board, so at some point it got wet under there and started corroding through the bottom of the tank).

 

[Crux]

Me too..lol. I love to do things myself. But one night of welding on a partially cleaned poop tank has realigned my outlook on this project. :lol:

Lol!! Interesting how this corrosion seems localized to area at welded elbow...almost like some acidic flux reaction?....other welds look pretty clean...

And Peggie, I have your book and have referred others to it....a very, very
helpful work..Thank You!

 

[Marco Flamingo]

I have the same boat as Barking Sands. My PO put in a 15 gallon plastic tank forward of the engine room bulkhead, sort of down in the bilge. It is long and skinny, fits the area okay but not perfect. Black water tankage is all aftermarket on these early 80's boats as they came with direct overboard heads. My tank install is easily the least professional modification to the boat.

Besides 15 gallons being on the small side (we exercise some restraint so it lasts 10 days of cruising) the other problem is that being installed in front of the engine room bulkhead resulted in some amateurish sawzall work to the bulkhead for placing the tank and hoses. I've been slowly reducing engine noise and that hacked ER bulkhead is a major impediment.

I've gone through all the online catalogs that I can find looking at stock replacements that will fit low between the stringers in the bilge and entirely in the engine room. Most are in the 25-35 gallon range. That would allow me to place the tank low and center, replace the cutout engine room bulkhead, and have only a couple of tight penetrations for the hoses. A custom tank would work, but it generally doubles the cost, so it would be an additional $300 for a few gallons increase. With 500 stock models available (it seems like), paying for a custom tank seems extravagant.

I agree with junking the SS tank. If you haven't looked inside, you don't know if you're really fixing anything worth fixing. A scrap yard will give you $0.70 per pound. Apply that to a new plastic tank.

I kept all of my research in a file on my computer as to which tank models would work. But of course I can't find the file right now. I'll keep looking.

 

[Arc]

You should be using Tri Mix For mig stainless welding. 75/25 is good for tig not for mig

 

[backinblue]

As Peggie pointed out, and I tend to agree with her, the tank may be that old, but maybe wasn't regularly used until the last decade or 2.

 

[HeadMistress]

I've gone through all the online catalogs that I can find looking at stock replacements that will fit low between the stringers in the bilge and entirely in the engine room. Most are in the 25-35 gallon range.


Why is that the only location for it?



--Peggie

 

[Barking Sands]

You should be using Tri Mix For mig stainless welding. 75/25 is good for tig not for mig

In research I read Tri Mix is preferred but you can do it with 75/25 with less than optimal conditions. It actually worked fairly well. I did not want to invest in another bottle to get Tri Mix for this project that was not likely to end up being used.